1. Field of the Invention
The present invention relates generally to a helical-scanning type of X-ray CT apparatus which scans an object to be scanned in a helical manner and, more particularly, to a helical-scanning type of X-ray CT apparatus which carries out the helical scanning for the object to be scanned by means of a movable gantry, without moving the object to be scanned.
2. Description of the Related Art
In the conventional helical-scanning type of CT apparatus, a table top of a patient couch mounting the object to be scanned thereon is continuously moved at a regular speed in a X-ray CT gantry dome including, for example, a X-ray tube and a detector both rotating continuously, so that a helical movement of a scanning section relative to the object to be scanned can be accomplished.
Recently, with the broad field of medical treatments with the application of the X-ray CT apparatus, there are demands for executing the X-ray CT scanning during a surgical operation for brain and inspecting while taking an angiography unit and the X-ray CT apparatus together in the interventional radiology (IVR) technique where a puncturing, an exploratory excision and a catheter handling are carried out with reference to the radiographic image of the object to be scanned.
However, it should be noted that there is raised the following problem in the application of the conventional X-ray CT apparatus to the field of medical treatment.
For example, in case of executing such an X-ray CT scanning during the brain surgical operation, it should be recognized a patient couch mounting the patient thereon is a table for surgical operation. It is general that the table for surgical operation is required to have a function of allowing the patient to be fixed into a desirable posture for the operation.
For example, in the brain surgical operation, the table is required to have a function of maintaining the patient's semi-sitting posture (i.e. Fowler position) where the only upper body of the patient is raised by 40 to 50 cm. Therefore, it is difficult in technique to allow the table for operation to have a function of feeding a tabletop for helical scanning.
Note, although there has been provided a patient couch which is commonly usable for the angiography unit and X-ray CT apparatus in the interventional radiology (IVR) technique, the patient couch has a problem of making a free manipulation for a tabletop heavier since the angiography unit is required to have a function of allowing the tabletop to be moved back, forth, right and left freely, while the X-ray CT apparatus is required to have a function of feeding the tabletop precisely for the helical scanning,